			15min:

SPECTRAL INHOMOGENEITY AS A DISCRETE, COUNTABLE ENTITY -- THE ROLE OF RESIDUAL ORTHOHYDROGEN MOLECULES ON THE ROVIBRATIONAL SPECTRA OF DOPANTS IN PARAHYDROGEN SOLIDS.

MARIO E. FAJARDO AND SIMON TAM, AFRL/PRSP, Bldg. 8451, Propulsion Sciences and Advanced Concepts Division, US Air Force Research Lab, Edwards AFB, CA 93524-7680..

We report high resolution (0.005 cm^-1) infrared (IR) absorption spectra of doped millimeters-thick parahydrogen (pH₂) solids with intentionally elevated residual orthohydrogen (oH₂) concentrations. In addition to the weakly-hindered rotor spectrum of isolated H₂O molecules, H₂O/oH₂/pH₂ samples exhibit a series of sharp (0.03 cm^-1 FWHM) absorption peaks in the 1593 to 1597 cm^-1 region which we show are due to H₂O-oH₂ clusters. We have also identified CO₂-oH₂ clusters as the source of the very sharp (0.007 cm^-1 FWHM) fine structure in IR spectra of CO₂/oH₂/pH₂ solids. The gradual evolution of the CO₂-oH₂ features with increasing oH₂ concentration raises the interesting notion of spectral inhomogeneity as a discrete, countable entity.